There are different instruments available for injection of dye or x-ray contrast medium into the uterine cavity. In order to seal the vaginal opening of the uterus (external os) some of the cannulas have an acorn which is pushed against the external os and insures leak proof application. Sometimes, however, the sealing of the external os fails.
In an attempt to overcome this problem, another instrument was developed. This instrument consists of two channels, one for injection of dye or x-ray contrast medium, and the second for inflating a balloon inside the uterine cavity. This structure seals the external os and prevents leaking. The disadvantages of the cannula with balloon instrument is its cumbersome construction and its high cost.